Flexible ducting is used in many mines for ventilation purposes and usually comprises a cloth tube which is supplied in lengths and joined between the lengths. Air is blown or drawn through the ducting to the required positions. In order for the ventilation to be efficient it is necessary that the ducting is substantially leakproof and that the joints are effective. The ducting itself is made from a fabric material such as nylon or terylene which is coated with a plastic material such as p.v.c. In certain cases the coating may also include anti static materials.
One form of jointing which has been used is that of two interlocking rings. At the end of each length of ducting the cuff has a flexible ring stitched to it. This can be squeezed so as to pass through an identical ring attached to an adjacent length of ducting. The first ring is then pulled back until it abuts behind the ring on the adjacent length. This type of jointing is cheap and is satisfactory as long as the ducting is continually in use and is not under longitudinal strain or subject to high pressure when the ends may step out of engagement. Also, when the pressure within the ducting falls and the ducting collapses the joints may come apart since one ring can fall back into the ducting and slip out of its adjacent end when ventilation is re-started.
Alternative forms of joint are known, for example from British Pat. Nos. 1,050,871 and 1,154,943 which use a draw string or the like to pull one end of the ducting tight round an adjacent end which is inserted into the first end. These alternative forms suffer from the disadvantages that since there are many pieces which are not integral with the ducting it is easy for one piece to become dislodged and lost and also that the cost of making the various pieces for the joint is relatively high. Furthermore, the drawstrings have been known to break and if the strings are pulled too tight they throttle the joint to reduce the size of the ducting at the joint. Added to these is the disadvantage that if the string is not secured sufficiently tightly or stretches the joint will be subject to a high leakage rate, or in the extreme case will part.